The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In the mechanical joining of substrates, for example in an automotive vehicle assembly process, substrates are joined to each other with an adhesive material along a joint and between the substrates. The adhesive material serves a number of functions, including providing an environmental seal, to increase the mechanical strength of the joint, and to compensate for part and assembly tolerances. In addition to the adhesive material, mechanical fasteners/fixings are also used to secure the substrates to each other, wherein the mechanical fasteners penetrate the substrates and the adhesive material to provide the primary structural joint and its strength.
Referring to FIG. 1, one form of fasteners/fixings used to secure the substrates to each other is a self-piercing rivet (SPR). Installation of an SPR generally involves driving the SPR 10 into substrates 11, 12 to be joined with an SPR tool, which includes a punch 14 and a gun nose 15. A die 16 is also provided on an underside of the lower substrate 12, and an adhesive 17 is applied between the substrates 11, 12 prior to installation as shown in step A. During installation, the gun nose 15 and the die 16 are forced together in step B, (compressing the adhesive 17 to a thickness typically less than about 0.2 mm), and the punch 14 forces the SPR 10 down such that the SPR 10 pierces the upper substrate 11 and flares into the lower substrate 12 as shown in step C. As the SPR 10 is forced into the substrates 11/12, the substrates 11/12 are plastically deformed, which draws air into the joint as shown, which is undesirable since air voids in the adhesive 17 can weaken the joint and be a source for environmental corrosion and a water leak path. These air voids remain when multiple SPRs are installed.
This issue of air voids in the adhesive in SPR joints, among other mechanical joining issues, is addressed by the present disclosure.